Split flap



June 9,1936. F. E. WEICK 2,043,275

' SPLIT FLAP Filed April 28, 1934 drranvsrs till Patented June 9, 1936 UNITED STATES SPLIT FLAP Fred E. Weick, Langley Field, Va. Application April as, 1934, Serial No. man

3 Claims.

(Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) The invention described herein may bemanui'actured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

Among the devices for increasing the maximum lift coeiiicient over that obtained with a conventional wing, the one most commonly used has probably been the trailing edge flap, which is deflected downward to increase the camber of the wing. Later developments resulted in the split-flap airfoil in whichthe rear portion of the airfoil is split into upper and lower sections and the lower section or,ifiapdefiected downward. In some instances, the flap is adapted to be moved to the rear as well as deflected downward in angle, giving in effect an 'increase in'area as well as in. camber. I

In the recent application of flaps to airplane wings, it has been necessary, either to use special ailerons (which have notbeen found as satisfactory as ordinaryfiap type ailerons) or to sacrifice a part of the performance desired from the flap, as by confining itto the portion of the wing inboard of; the ailerons. As far as known, however,;fthere; has been no successful development, prior to ;:the invention herein disclosed, of a combination. of a high lift device and a device folith obtaining of lateral control which will give the full. advantages of a well located split flap as well as those of conventional ailerons of narrow chord.

It is, therefore, an object'of the present invention to provide an arrangement permitting the use of conventional ailerons together with a full-span split flap located in the most effective position for increasing the lift coeflicient when deflected. This is' accomplished by providing, in an airplane wing, .the combination of conventional fiap-type-tr'ailing edge ailerons and a split flapv which. when retracted, fits into the under surface of; the wing ahead of the ailerons but whenextended has its. trailing edge moved to the rearfasfwell as "downward so that it; is,

approximately'intheposition giving the maxi mum lift coemcient. f

In the drawing Figure 3 is a similar view of the airplane wing,

with the splitflap in extended position.

Figure 4 is a sectional view on line 4-4 of Figure 2.

Figure 1 is a diagrammatic view bf "a. te ted". Clark Y airfoil. wlth split flap arrangement;-

Figure 5 is a sectional view on line 5-5 of Figure 3, and

Figure 6 is a view showing a flap of modified cross section.

In determining the most eflicient position of the split flap for increasing the lift coefficient of the wing tests were made on a model wing as part of a series on high-lift devices in the N. A. C. .A. 7x10 foot wind tunnel. Lift, drag, and pitching moment were measured for a basic Clark Y airfoil equipped with split flaps of three different sizes. Each flap could be rotated downward, about an axis at its front edge. The tests were made with a range of angular deflections ateach of several fore-and-alt locations of the axis along the basic wing chord. The model wing had a chord of 10 inches and a span of inches.

The three sizes of flaps tested had chord lengths of 0.20 c., 0.30 c., and 0.40 c.; 0 being the chord of the basic wing. I The 0.20 c. flap was tested with its axis at 0.80 c., 0.90 c., and 1,0 0. fromthe leading edge, the 0.30 c. flap with its axis at 0.700. to 1.0 c., and the 0.40 c. flap with its axis M060 0. to 1.00., all with even 0.10 0. intervals. The flaps could locked in any angular position and the tests were made with the flaps deflected at 15 intervals, or less where necessary, over a sufficient range to determine the highest value of C1. max for each hinge location.

The highest lift coeificient obtained by depressing the split flaps with the flap axis in original location, that iswithout moving the axis jto the'rear-was very nearly the same for all three flap sizes and were somewhat higher than those given by conventional trailing edge flaps.

With each siaeof flap, the maximum lift coefficient was increased'asthe flap axis was moved back to the 0.90c.,p0sition. With the 0.20 c.

flapiit continued to increase slightly as the axis wasfgmove'd tojthe trailing edge,,but withthe larger. sized flaps-the values were slightly lower for the "trailing edge axis location than for the" one 'at0.90 c. The highest valuesof CL max for the three flaps were found to beas follows:

Highest Axis loca- Flap size 1L m; tion angle 0.20 c 2. 27 1.00 c. as" i .300 245* .93 0. 62. 40 L 2. 52 .90 0. 54

The highest value, which represents an increase of 98 per cent over the value of 1.27 for. .Y

the plain wing, was obtainedwiththe 0.40 c.

flap., 1

The particular feature of the split flap airfoil, forming the subject matter of the present invention, which is novel and different from previous ones, is the fact that ordinary ailerons are used over the same part of the span as a welllocated split flap which may extend across the entire wing span. For present purposes, the invention will be described with reference to its ,embodiment in a basic Clark Y airfoil equipped with a split flap extending across the entire wing span and having a chord length of 40 per cent of the basic wing chord. The airfoil l is provided with the conventional trailing-edge ailerons 2 of narrow chord and, as shown in Figures 2 and 4, the flap 3 when retracted fits into a recess 4 in the undersurface of the wing ahead of the conventional ailerons. The split flap shown in Figures 2 to 5 inclusive is of flat plate type beveled at the trailing edge and when closed it is flush with the lower surface of the airfoil. In this condition, the wing with ailerons operates in the normal manner of present conventional airplanes. If desired, the ailerons may be balanced to reduce the control forces by any ordinary means, such as the inset hinge.

When the split flap is deflected, to give lower speed and steeper glide for landing, it is moved to the rear, as shown in Figures 3 and 5, putting it in approximately the most effective location, as diagrammatically represented in Fig. 1, and also making it relatively easy to operate. Tests conducted in the 7 by 10 foot wind tunnel show that the conventional ailerons with any of the commonly used deflection linkages (equal up and down or differential) will give reasonably good rolling control at angles of attack below the stall with the flap deflected in the position shown.

One manner of supporting the split flap and guiding its motion in a suitable manner is illus-' trated in Figures 4 and 5 which show one of two or more similar supports that would be used at different places along the span. Each support includes separate converging rails or tracks 5 and 6 in the split portion of the wing ahead of the ailerons and a bracket 1 on the split flap fitted with two rollers 8 and 9 which run in the tracks 5 and 6. When some linkage (not shown) 18 used to push the flap to the rear, the rear portiondof the flap is deflected simultaneously downwar All of the better known combinations of high lift devices and devices for the obtaining of lateral control fall short of giving the full maxilift coefficient. The split flap is, in general practice, located at the rear edge of the wing when retracted, making it impossible to use normal conventional ailegms on the portion of the wing covered by the flap. In split flap arrangements heretofore designed to permit the use of conventional ailerons, the latter have in some instances been pivotally mounted on a trailing portion of the flap and in other instances have been mounted in the usual manner on thawing with the split flap movable about an axis fixed at a distance forwardly oi the trailing edge of the wing so that the flap, when retracted, fits in the undersurface of the wing ahead of the ailerons. Such an arrangement permits the use of conventional ailerons but the deflected flap is necessarily in an ineficient position for increasing the lift coeflicient of the wing. It gives about the same advantage as the arrangement in'which ordinary ailerons are used on the outer portions of a wing and the flap is confined to the portion of span inboard of the ailerons.

In the arrangement of the present invention, as herein disclosed and illustrated, the flap is not only retracted ahead of the ailerons permitting the use of conventional ailerons, but, when deflected is moved to the rear as well as downward and can be located in the most effective position for increasing the lift coefficient of the wing. Thus, it is the only arrangement permitting the use of conventional ailerons together with a full-span split flap located in the most effective position for increasing the lift coefiicient when deflected.

The invention is not limitedto a flap of the flat-plate type nor to any particular shape of flap. As shown in Fig. 6, the flap 32 may be of airfoil section and located with a slight gap In between it and the main portion of the wing when the flap is deflected.

Having thus described the invention, what is claimed as new is:

1. An airplane wing having cut-outs in its trailing edge portion for the reception of conventional flap-type trailing-edge ailerons and having a rear portion forwardly of the cut-outs split to provide an upper rigid section and a lower movable flap section, the said movable flap sectino being rotatable downwardly about an axis at its leading edge and having the flap axis movable to each of several fore-and-aft locations along the basic wing chord, including an aft location in which the flap is deflected downwardiy and directly below the ailerons with its leading edges substantially at the front edge of the cut-outs and its trailing edge disposed rearwardly beyond the cut-outs.

2. An airplane wing having cut-outs in its trailing edge portion for. the reception of conventional flap-type trailing-edge ailerons and having a full span split flap fitting into the undersurface of the wing ahead of the cut-outs when retracted, said flap being movable to the rear as well as downward when deflected to place it in angular position with its leading edge substantially adjacent the front edges of the cutouts and with its trailing edge below and rear- 4 wardly beyond the trailing edge of the wing to provide a maximum lift coefiicient without interference with the operation of the ailerons, and means within the wing and between the latter and upper surface of the split flap for supporting the split flap and guiding its motions of retraction and deflection.

3. An airplane wing having cut-outs in its trailing edge portion for the reception of conventional flap-type trailing-edge ailerons and having a full span flap on the underside of the wing having an original axis location along the basic wing chord forwardly of the trailing edge of the wing to permit the flap to be retracted into the wing ahead of the cut-outs, said flap being rotatable downwardly about its axis and shiftable to move the flap axis rearwardly to a position immediately forward of the said cutouts, and means for supporting the flap and guid- 6 ing its motion including separate converging tracks fixed to the wing inwardly of the top and bottom, surfaces thereof and forwardly of the cut-outs at different places along the span and brackets on the upper side of the flap adjacent the leading edges thereof and provided with rollers which run in the said converging tracks.

FRED E. WEI-CK. 

